Control of Crystal Morphology for Mold Flux During High-Aluminum AHSS Continuous Casting Process

Abstract

In the present manuscript, the efforts to control the crystal morphology are carried out aiming at improving the lubrication of lime-alumina-based mold flux for casting advanced high-strength steel with high aluminum. Jackson a factors for crystals of melt crystallization in multi-component mold fluxes are established and reasonably evaluated by applying thermodynamic databases to understand the crystal morphology control both in lime-alumina-based and lime-silica-based mold fluxes. The results show that Jackson a factor and supercooling are the most critical factors to determine the crystal morphology in a mold flux. Crystals precipitating in mold fluxes appear with different morphologies due to their different Jackson a factors and are likely to be more faceted with higher Jackson a factor. In addition, there is a critical supercooling degree for crystal morphology dendritic transition. When the supercooling over the critical value, the crystals transform from faceted shape to dendritic ones in morphology as the kinetic roughening occurs. Typically, the critical supercooling degrees for cuspidine dendritic transition in the lime-silica-based mold fluxes are evaluated to be between 0.05 and 0.06. Finally, addition of a small amount of Li 2 O in the mold flux can increase the Jackson a factor and decrease the supercooling for cuspidine precipitation; thus, it is favorable to enhance a faceted cuspidine crystal.

Crystallization Kinetics and Structure of CaF₂–CaO–Al₂O₃–MgO–TiO₂ Slag for Electroslag Remelting

“…The SEM observations showed the primary crystalline phases in the slag were faceted morphology, 16) indicating that the crystallization of the crystalline phase is controlled by interfacial reaction. 35,36) It can be concluded that the crystallization of primary crystalline phase (11CaO•7Al 2 O 3 •CaF 2 ) in the 37) but different from the findings that the crystallization of slag is controlled by element diffusion. [38][39][40] Figure 6 shows the room temperature Raman spectra of the glassy samples with varying TiO 2 contents.…”

Investigation on the Slag-Steel Reaction of Mold Fluxes Used for Casting Al-TRIP Steel

“…Non-linear fitting of SiO 2 content in both slags through Origin software is shown in Figure 10 of the crystalline phase. The crystals tended to be more faceted and anisotropic when their Jackson α factor increased [20]. The main crystalline phases and their corresponding melting temperature and Jackson α factors were shown in Table 3.…”

“…Many attempts based on conventional slag still find it difficult to avoid the slag-steel reaction effectively. Therefore, some researchers began to explore the study of non-reactive or weakly reactive slag [6,[14][15][16][17][18][19][20][21]. Among them, Wang et al [16,17] studied the effect of various oxide additions on the crystallization behavior and heat transfer properties of the CaO-Al 2 O 3 system continuous casting slag and provided some guidelines for the design of a reasonable CaO-Al 2 O 3 system slag.…”

“…Cho et al [18] designed the CaO-Al 2 O 3 based slag for continuous casting of 1.45% Al steel and found that the reactivity of Equation (1) was reduced significantly, resulting in a certain improvement of the slab quality. Seo et al [19,20] focused on the lubrication of a solid layer of slag used for high Al-AHSS (Advanced High Strength Steel) steel and proposed to control the crystalline morphology by Jackson α factors. It was found that the crystallization at the slag film was too strong to affect the lubrication, which ultimately led to defects in the slab.…”

Review of Mold Fluxes for Continuous Casting of High‐Alloy (Al, Mn, Ti) Steels

“…Recently, based on previous research, Jackson first established a theory to explain the solid–liquid interface morphology and proposed the Jackson α factor parameter to predict the metal crystal morphology . Guo et al introduced a thermodynamic method to estimate the Jackson α factor of a crystal in multicomponent mold fluxes, combining the previous findings and the FactSage thermodynamic database . The results revealed that CaF 2 , CaO · x Al 2 O 3 , CaO · y B 2 O 3 , and 3CaO · 2SiO 2 · CaF 2 precipitated in mold fluxes show different morphologies due to their different Jackson α factors and the precipitated crystals tend to be more faceted and anisotropic with increasing the Jackson α factors.…”